通过减少离频位移来改进基于 Bloch-Siegert 的 B1 映射。
Improved Bloch-Siegert based B1 mapping by reducing off-resonance shift.
机构信息
Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
出版信息
NMR Biomed. 2013 Sep;26(9):1070-8. doi: 10.1002/nbm.2920. Epub 2013 Jan 28.
An MRI method based on the Bloch-Siegert (BS) shift phenomenon was recently proposed as a fast and precise way to map a radio frequency (RF) transmit field (B1(+) field). For MRI at high field, the mapping sensitivity of this approach was limited by tissue heating associated with a BS irradiation pulse. To mitigate this, we investigated the possibility of lowering the off-resonance frequency of this pulse since theoretical analysis indicated that the sensitivity of Bloch-Siegert based B1(+) mapping could be substantially improved when irradiating closer to resonance. Using optimized irradiation pulse shape and gradient crushers to minimize direct excitation effects, in vivo experiments on human brains at 7 T confirmed improved sensitivity with this approach. Improved sensitivity translated into an 80% reduction in B1(+) estimation errors without increasing tissue heating. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
最近提出了一种基于布洛赫-西格特（Bloch-Siegert，BS）位移现象的 MRI 方法，用于快速准确地绘制射频（RF）发射场（B1(+)场）。对于高场 MRI，该方法的映射灵敏度受到与 BS 辐照脉冲相关的组织加热的限制。为了减轻这种情况，我们研究了降低该脉冲的离频频率的可能性，因为理论分析表明，当辐照更接近共振时，基于 Bloch-Siegert 的 B1(+)映射的灵敏度可以大大提高。使用优化的辐照脉冲形状和梯度破碎机来最小化直接激励效应，在 7T 下对人脑进行的体内实验证实了这种方法的灵敏度提高。灵敏度的提高转化为 B1(+)估计误差减少了 80%，而没有增加组织加热。2013 年发表。本文是美国政府的工作，在美国属于公有领域。
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